In cytology, an automated imaging system is used to analyze cellular material contained on a slide or other biological specimen carrier. For example, an imaging system might be used to help a cytotechnologist analyze a Pap smear slide. Preparation of a Pap smear slide involves scraping cells from a woman's cervix and depositing those cells on a slide. The slide is then reviewed by a cytotechnologist who screens the slide for cancerous or precancerous cells. This review can be done more quickly and more accurately if an automated imaging system first identifies objects (portion of the specimen) on the slide that are likely or more likely to be cancerous, and directs the cytotechnologist's attention to those identified objects.
FIG. 1 generally illustrates one known automated imaging system 10 that may be used to analyze Pap smear slides and other cytological specimen slides (generally illustrated in FIG. 2), available from Hologic, Inc., 250 Campus Drive, Marlborough, Mass. 01752. In particular, the system 10 is configured for imaging and presenting a biological specimen 12 located on a microscope slide 14. The system 10 includes an imaging station 20 that is configured to image the specimen 12 on the slide 14, which is typically contained within a cassette (not shown in FIG. 1) along with other slides. During the imaging process, slides 14 are removed from the respective cassettes, imaged, and returned to the cassettes in a serial fashion.
One known imaging station 20 includes a camera 22, a microscope 24, a motorized stage 26 and a light source 28. The slide 14 is mounted on the motorized stage 26, which scans the slide 14 relative to the viewing region of the microscope 24, while the camera 22 captures images of various regions of the specimen 12. The motorized stage 26 tracks the x-y coordinates of the images as they are captured by the camera 22. The x-y coordinates tracked by the stage 26 may be measured relative to one or more fiducial marks 16a-c (generally fiducial mark 16) affixed to the slide 14. A fiducial mark 16 may be a rectangular patch of paint that is applied to the slide 14 using silk screening methods. One corner of the fiducial mark 16 may be considered to be the mark's 16 location.
Image data 23 generated by the imaging station 20 is processed by a server 30 that includes suitable hardware and software (e.g., one or more processors 31-33) to select and store identified objects of interest (OOIs), which are arranged in Fields of Interest (FOI) of the imaged biological specimen 12. The OOIs may then be presented to a cytotechnologist, who can then review them using one or more reviewing stations 40A-C (generally referred to as reviewing station 40) and that includes a microscope 44 and a motorized slide holder or stage 46. During the review process, the slide 14 is mounted on the motorized stage 46, which moves the slide 14 relative to the viewing region of the microscope 44 based on the routing plan and a transformation of the x-y coordinates of FOIs are obtained from memory 34. Coordinates of the slide 14 determined during the reviewing process are correlated to the x-y coordinates of the slide 14 during the imaging process using fiducial marks 16. The motorized stage 46 moves according to the transformed x-y coordinates of the FOIs, as dictated by the routing plan.
Typically, slides are labeled with a number, bar code, or other identification. This identifying information can either be manually entered into an imaging system by a human operator, or it can be read by an optical character recognition (OCR) camera or bar code reader. In the latter case, the imaging system will contain at least two imaging devices. One imaging device views the microscopic features of the slide, such as cells. The other imaging device views the slide on a macroscopic level, in order to read the identifying information.
An automated imaging system will typically generate some data associated with each slide it processes. This data may be stored or reported to the operator. It is essential that the data be associated with the proper slide. An imaging system may be designed such that during slide processing, the operator may remove a first slide that has been loaded into the system and replace it with a second slide. However, if the system cannot detect that the first slide has been replaced by the second slide, the system may incorrectly associate data from the first slide with the second slide, or vice versa and, therefore, it may be necessary to discard the data.
There are several different ways in which an imaging system can detect when one slide has been replaced with another slide. Some automated imaging systems include a custom-made slide holder that incorporates a slide removal sensor. Systems may also incorporate an OCR reader or bar code scanner to read identifying information of the slide before and after it is processed to ensure that the slide was not swapped with another during processing. Such custom components, however, increase the cost and complexity of imaging systems.
Further, certain imaging may not include a slide removal sensor or an OCR reader or bar code scanner, e.g., due to cost, space and integration issues. With these types of systems, it may be difficult to confirm that certain data is associated with a particular slide and that one slide has not been swapped with another during processing.